Virus Flashcards
(23 cards)
Infection mechanism of a virus
Virus invades mucosal barrier in the body
- Implantation:
Proteins of the outer membrane of the virus binds to a specific receptor of the host’s cell. - Penetration:
Activation of the receptor allows virus to enter the host’s cell through endocytosis. - Uncoating
If the virus contains a capsule, this is shed. The genetic material of the virus is released to into the host’s cell. - Replication
Virus forms it’s viral mRNA using either it’s own or the host’s RNA polymerase.
This forms proteins which allow the formation new viruses and also new genetic material. - Release:
New viruses are released in an envelope made from the host’s cell material.
General structure of a virus.
Genetic material, DNA or RNA, enclosed in a capsid.
DNA and RNA can be double or single stranded. Can also be positive or negative.
Nucleocapsid, composed of nucleic acid and capsid, is surrounded in an enveloped derived from its host’s cell.
Positive/ negative genetic material.
Positive- when the nucleotide sequence of DNA or RNA has the same sequence as mRNA.
Negative- when the sequence is complementary to mRNA. Therefore it has to be transcribed to mRNA first before creating proteins.
Virulence
The severity of disease caused by a virus. This can be affected by:
Cell tropism
The response from the host
The efficiency of its replication
Its interaction with the host
Cell tropism
These are the features of a virus that allows it to target specific tissue- adaptations that allow increased virulence.
Viruses can only affect the cells that have receptors that bind to its surface proteins- Susceptibility.
Host cells must also have the correct enzymes to allow the production of viral proteins- Permissivity.
Susceptibility
Virus requires its host cell to have the correct receptors that allows viral implantation.
Permissivity
Host cells must obtain the correct enzymes and transcription factors to allow the successful production of viral proteins.
The outcome of viral infections
Causes cells to be dysfunctional; affects metabolic and regulatory processes.
Can release toxic productions which cause:
Cell necrosis
Further viral replication.
Cell lysis
Latency
When a virus is present in a host but is not active.
Does not replicate genetic material until triggered by a specific factor.
Includes:
HSV (herpes simplex virus type 1/2) reactivation- causes fever, blisters.
Retrovirus can cause cell to be cancerous.
Different methods of viral transmission
Through blood into organ systems
Through neurones into organs in the CNS
Vector (yellow fever)
Droplet (Influenza)
Transplacental (Zika)
Oral contact (Hep A)
Sexually transmitted (HIV)
Exogenous infection
When the virus from outside the host infects the host by breaking through physical barrier..
Endogenous infection
When there is a re-activation of a latent virus present in the host.
Usually occurs when the immune system has been suppressed.
Includes
Shingles virus (VZN)
HSV
CMV (Cytomegalovirus)
Acute vs Chronic viral infections.
Acute: Immediate onset of infection. When there is no equilibrium between the virus and the host cells. There is a constant change in both factors.
Chronic: Persistent infection. When there is an equilibrium between the viral and host cells.
Different methods of showing that a virus is the causative agent. (5)
- Antigen detection
- Serology (antibody response)
- Using cell cultures
- Detection of the viral nucleic acid
- Microscopy
Using microscopy to test for viruses
Allows viruses to be clearly seen but:
Electron microscopes are very expensive
Require expertise
Requires a high viral copy in sample.
Using cell cultures to test for viruses
Viruses are grown in different cell lines, not all viruses can be grown in a cell culture.
A culture of inoculated and uninoculated cells are grown and compared under a microscope.
The virus is recognised by its cytopathic effects.
HOWEVER:
The method is slow for diagnosis and has limited use.
Using immunofluorescence to detect viruses.
Detects the antigen on the virus:
Specific monoclonal antibodies are created for a known antigen on the virus.
Antibody is attached to a fluorescent marker and placed in sample.
A fluorescent microscope is used to detect the antigen present.
HOWEVER:
This method is limited to only a certain number of antigens.
Requires expert personnel to carry out.
Serology
Detects the presence of antibodies in the serum.
ELISA test:
A substrate that changes colour when cleaved by the enzyme attached to the second antibody.
2nd antibody is attached to an enzymes. If patient’s serum contains the antibodies, colour change occurs.
Viral nucleic acid detection.
Uses PCR to amplify viral sample.
PCR uses a primer that has a specific known sequence of a virus’s genetic material.
Methods of viral prevention
General measures: gloves, masks
Specific measures:
Vaccines
Chemoprophylaxis
Immunoprophylaxis
Methods of treatment of viral infections.
General: antipyretics
Treats fevers by decreasing body temperature. Less hospitable for viruses.
Specific: antiviral medication.
Antiviral drug for HIV
HAART, Highly active antiretroviral therapy, does not cure HIV. Only reduces viral load.
Highly active antiretroviral therapy.
Antiviral drugs for Influenza
Tamiflu and others
